The invention relates to a housing for a piezoelectric actuator arrangement.
Piezoelectric actuators are commonly used in fuel injectors to control movement of a valve needle within a fuel injector nozzle body, movement of the valve needle being used to control the delivery of fuel into an engine cylinder or other combustion space. The distance through which the valve needle is moved is controlled by controlling the energization level, and hence the axial length, of a piezoelectric stack. The energization level of the piezoelectric stack is controlled by applying a voltage across the stack by means of an electrical connector which is connected to a voltage supply, and connecting leads which connect the piezoelectric stack to the electrical connector.
Conventionally, the piezoelectric stack is mounted directly in the fuel injector housing. During assembly of the fuel injector, external loading of the injector body can result in vibration of the piezoelectric stack which can damage the connecting leads. Furthermore, during use of the fuel injector, wear of the end caps of the piezoelectric stack and thermal expansion effects can cause axial movement of the piezoelectric stack within the injector body which can cause the connecting leads to vibrate and fray. In order to alleviate these problems, it is known to connect the connecting leads to sliding contacts which are arranged on the piezoelectric stack. However, the sliding contacts are prone to oxidisation which can degrade performance. It is further desirable to isolate the piezoelectric stack and its associated connecting leads from fuel or other liquids.
It is an object of the present invention to provide a housing for a piezoelectric stack which enables the aforementioned problems of the prior art to be alleviated.
According to the present invention, there is provided a housing for a piezoelectric actuator arrangement including a piezoelectric stack, the housing comprising a first housing portion for connecting leads which are electrically connected to the piezoelectric stack and a second housing portion for the piezoelectric stack, the first and second housing portions being integrally moulded and being formed from material which permits flexing of the first housing portion and the connecting leads.
The invention provides the advantage that, during assembly of a valve or fuel injector containing the actuator arrangement, a degree of flexing of the connecting leads is permitted which prevents damage being caused to the connecting leads when the housing, including the piezoelectric actuator arrangement, is clamped or secured in position. In addition, during use of the valve or fuel injector, vibration and axial movement of the piezoelectric stack due to thermal expansion effects and wear of the piezoelectric stack end caps does not lead to damage of the connecting leads as the connecting leads are able to flex to absorb any such vibrations or movements.
Conveniently, the housing may be formed from a polymer material.
Preferably, the housing includes a third housing portion housing an electrical connector, the third housing portion being integrally moulded with the first and second housing portions, the electrical connector being provided with electrical terminals for connection with the connecting leads. By integrally forming the third housing portion for the electrical connector with the first and second housing portions, the need for additional sealing of the electrical terminals is removed.
The second housing portion may be a sleeve member.
The actuator housing may include the piezoelectric stack.